Didemnin B is a macrocyclic depsipeptide isolated from a species of marine tunicate. Didemnin B exhibits potent anti-viral, immunosuppressive, and anti-tumor activities in vitro and in vivo, and was the first marine natural product to enter clinical testing against human cancers (Li et al., 1992, Studies in Natural Products Chemistry, 10:241-302; Sakai et al., 1996, J. Med. Chem. 39:2819-2834; Wipf, 1995, Chem. Rev. 95:2115-2134). Didemnin B is a didemnin, a family of compounds which potently inhibit protein synthesis and cell cycle progression, and induce more rapid apoptosis than any other natural products that has been isolated to date (Grubb et al., 1995, Biochem. Biophys, Res. Commun. 215:1130-1136; Johnson et al., 1996, FEBS Lett. 383:1-5; Johnson et al., 1999, Immunol. Cell Biol. 77:242-248; Johnson et al., 1999, J. Cell. Biochem. 72:269-278). Other members of this family of compounds, including didemnin M and dehydrodidemnin B, exhibit cytotoxic and cytostatic effects as well.
Tamandarin A (also designated {(2S)Hiv2}didemnin B) is a naturally occurring didemnin congener which has recently been isolated from a marine tunicate. Tamandarin A exhibits biological activity which is analogous to the activities exhibited didemnin B. For example, tamandarin A is a potent inhibitor of protein synthesis, cell growth, and tumorigenesis. Tamandarin A exhibits greater in vitro activity against pancreatic carcinoma than does didemnin B (Liang et al., 1999, Org. Lett. 1: 1319-1322). A significant limitation on use of tamandarin A, either for research or for practical applications, is the limited supply of tamandarin A that is available from natural sources and the difficulty and expense of isolating this product. A need exists for a method of synthesizing tamandarin A and other didemnin analogs (including dehydrodidemnin analogs).
Despite the potency of didemnin B in isolated studies, its clinical effectiveness is hampered by side effects associated with therapeutic doses of the compound. As with many anti-proliferative agents, didemnin B exhibits a relatively narrow therapeutic window. Although didemnin M and dehydrodidemnin B exhibit improved therapeutic potential, relative to didemnin B, a need still exists for anti-proliferative agents which exhibit less toxicity at a therapeutic dose (i.e. didemnin analogs having a greater therapeutic index).
The present invention satisfies the needs set forth above.